The present invention relates to a damper assembly for controlling the flow in coal pipes supplying burners in furnaces and boilers. Particularly, the invention relates to a new and improved boiler blade which is sized to effectively block only a part of the entire cross-section of a coal pipe.
A pulverized coal-burning boiler has one or more pulverizers which are used to grind lumps of coal into particulates with a certain desired size distribution. Feed pipes ranging from 8xe2x80x3-24xe2x80x3 in diameter typically transport the airborne pulverized coal (PC) to each burner in feed pipes ranging from 8xe2x80x3-24xe2x80x3 in diameter. The number of burners fed by one pulverizer can be anywhere from 2-13 which are supplied by as many pipes carrying the pulverized coal.
In order to attain thermal efficiency and to maintain close control of stock emission in a multi-burner boiler system, it is essential to maintain a good balance among all the burners. The flow of pulverized coal is the single most important process variable that needs to be controlled to achieve balanced operation among several burners. The imbalance needs to be corrected to insure efficient combustion. To balance the burners, it is necessary to measure and control the coal flow rate and the primary and secondary airflow rates to each burner. Balanced burner operation requires that the mass flow rate of both air and pulverized coal be the same among all the pipes leading to the burner within certain operating limits.
Common industry practice is to install a plate controlling the full area of the pipe or conduit when only a part of this area needs to be blocked to balance flow to multiple burners.
U.S. Pat. No. 5,685,240 to Briggs discloses a pulverized coal flow control system including a frame sealingly secured to an outside surface of the coal pipe around a window opening formed on one side of the pipe. A rotatable damper plate inserted through the opening has a cross-section comparable with a cross-section of the coal pipe and is provided with an orifice opening at its center. The plate is adapted to rotate to vary the flow cross-section of the orifice opening for controlling the flow of coal and primary air to a burner.
The installation of such plate can be quite costly for two reasons. First, the window opening formed in the side of the pipe should be large enough to receive the damper plate, and second, the manufacture of the central orifice requires a specifically designed piece of equipment. Further, because the outer diameter of the damper plate is only insubstantially less than an inner diameter of the pipe, when the plate is tilted, the flow is directed against an inner surface of the pipe. This, in turn, may cause rapid deterioration of the pipe both because of the high velocity of the flow impinging upon the inner surface and high temperatures.
U.S. Pat. No. 4,459,922 to Chadshay discloses a plurality of plate segments pivotally mounted in a bracket, which is fastened between two conduit sections through which air-entrained pulverized coal flows, the segments being pivoted by an operator from external the conduit. Each of the plate segments has a complex arcuate cross-section and is pivoted eccentrically between the minimum and maximum of restriction to the coal/air flow through a conduit.
The complexity of this system makes it to be rather expensive. Furthermore, because of the numerous tilting positions each segment can direct a fraction of the flow against the inner surface of the conduit which may damage its inner surface for the reasons discussed above.
Accordingly, there is a need for a simple, cost-efficient damper assembly which does not require complicated installation. A damper assembly including a damper plate blocking a percentage of the entire cross-section of a coal pipe is desirable, as is a damper assembly easily controllable to vary a percentage of the blocked cross-section of the coal pipe.
The present invention solves the problems associated with the prior art by providing an a damper assembly having at least one generally flat damper plate having a length, which is substantially less than an inner diameter of a conduit, and a width, which is substantially less than this inner diameter. Rotating of the blade, manufactured in accordance with the invention, can adjust the flow from no change to about 75% of full flow. The dimensions of the damper blade allow insertion of the assembly through a small opening in a wall of the conduit. The opening""s diameter can be substantially the same as the width of the plate. In contrast, the known prior art assemblies typically necessitate formation of a large opening receiving damper plates designed to control the full area of the conduit.
In accordance with another aspect of the invention, the shape of the damper plate can be modified to effectively block a percentage of the full area greater than a percentage blocked by a flat damper blade. Particularly, an angle can be added to at least one of opposite blade sides facing the flow. Preferably, both opposite sides are angled to even further increase the area of the conduit that can be blocked, without however enlarging the opening.
In accordance with another aspect of the invention, a damper assembly includes a plurality of damper blades angularly displaceable relative to one another to effectively block a larger cross-section of the conduit when they are spaced from one another. One of the embodiments allowing the angular displacement of the blades includes a pin traversing proximal ends of these blades. Still another embodiment can be implemented by pivotally attaching the central regions of the blades. In accordance with the main concept of the invention, the blades have substantially a uniform width which is small relative to the inner diameter of the conduit. As a consequence, an opening provided in the wall of the conduit is dimensioned substantially equal to the cumulative thickness of the blades in a rest position, wherein the blades are aligned.
Displacement of the damper blades can be utilized by employing a variety of methods. Thus, for example, actuating a screw that has its distal end urging against a cam surface which is formed either on a proximal end of the damper blade or in its central region can move the blade relative to the other blades in a desirable angular position. In order to displace this blade in its initial position, the assembly can be pulled back from the conduit through a sleeve attached to the conduit""s wall and having an inner diameter which is insubstantially greater than the width of the blade. Alternatively, another screw can be actuated to impart the motion upon the cam surface of the displaced blade in a direction towards the blade""s initial position. The screws can be actuated manually, electrically or pneumatically.
Accordingly, an object of the present invention is to provide a damper assembly for controlling the flow of fluid transported solid particles.
A further object of the present invention is to provide a damper assembly which is simple in design, rugged in construction, and economical to manufacture.
Another object of the present invention is directed to a damper assembly having a single damper blade effectively blocking a percentage of the full are of a conduit which is traversed by the flow of fluid transported solid articles.
Yet another object of the invention is to provide a damper assembly including a multiplicity of blades which are angularly displaceable relative to one another to vary a percentage of the full area of the conduit traversed by the flow.
Still another object of the invention is to provide a damper assembly with an angled damper blade to effectively block a large area of the conduit.
For a better understanding of the invention, and the operating advantages attained by its use, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.